Marine depredation (removal of fish from longline hooks by marine predators) is a growing issue in fisheries around the world. Within the CCAMLR management killer whales and to a lesser extent sperm whales cause greatest disruption to longline fishing activities for toothfish (Dissostichus sp.). Several measures have been developed and tested over the years to mitigate depredation by toothed whales, which include devices such as acoustic harassment devices (AHDs) emitting a deterring sound, the physical protection of the catch by nets, hooks or wires or changes in fishing practise such as moving to a different area when orcas are present, changing offal dumping practises or using lines of different length. However, deterrents and in particular acoustic deterrents have the potential to also affect non-target species such as fish, diving birds or pinnipeds. The different mitigation measures employed in the CCAMLR management area and their potential for disruption both in target and non-target species are reviewed below.
Dr Chris Darby